The present invention relates to a lubricating grease composition and more particularly to a lubricating grease composition which, when enclosed in a spindle bearing which is one of parts of various motors or the like or a rolling apparatus for machine tool or the like which oscillates at a small stroke, exhibits excellent lubricating properties and provides drastic improvements in resistance to fretting developed by repeated impact and oscillation caused by exterior oscillation as occurring during transportation and dropping impact developed by dropping during transportation and low torque properties.
The present invention also relates to a rolling bearing land a rolling apparatus which comprise the foregoing lubricating grease composition enclosed therein to provide improvements in fretting abrasion properties, impact resistance and low torque properties.
Various kinds of greases to be sealed in a ball bearing for a spindle motor have been developed conventionally for a recording device such as a hard disc of a computer, and a CD-R. The present inventor has proposed a lubricating grease composition containing 50 to 100% by weight of a carbonic ester compound with respect to a base oil, and a lithium soap as a thickener, aiming at a low friction coefficient and prolongation of a sound life (JP-A-2000-26875). Moreover, a lubricating grease composition synthesized from a carbonic ester compound, a hydroxide of an alkaline metal or an alkaline earth metal, and a higher fatty acid having 10 or more carbon atoms or a higher hydroxy fatty acid having one or more hydroxyl group and 10 or more carbon atoms, aiming at little dust generation (scattering), a small torque, the excellent sound characteristics, and a long life, is also known (JP-A-2000-63874).
Linear guide devices such as linear guide and ball screw are widely used for machine tool, etc. These rolling apparatus are filled with a grease for lubrication. Most ordinary greases merely comprise a high viscosity oil as a base oil but are free of additives other than rust preventive.
A rolling apparatus filled with a conventional high viscosity base oil-containing grease exhibits a satisfactory durability when it makes a reciprocating motion at a great stroke but is latently disadvantageous in that when it makes a reciprocating motion at a small stroke, i.e., oscillatory motion, it undergoes fretting abrasion that deteriorates the durability thereof.
A rolling bearing for use in hard disc or the like, too, is required to have resistance to fretting abrasion developed by repeated impact and oscillation caused by exterior oscillation during transportation. Such a rolling bearing has also been required to attain the reduction of the entire size thereof or have improvements in rotary properties such as rotary speed, torque and acoustic properties and have resistance to dropping impact.
In view of the circumstances, the invention has been achieved, and an object thereof is to provide a lubricating grease composition capable of providing the excellent lubricating characteristics, fretting resistance characteristics, and impact resistance characteristics.
Another object of the invention is to provide a rolling bearing and a rolling apparatus having improved fretting abrasion resistance, impact resistance and low torque properties.
The object can be achieved by a lubricating grease composition according to the invention, having a basic grease composition containing a synthetic oil as a base oil, and a lithium soap as a thickener, wherein 5 to 10% by weight with respect to the basic grease composition total amount of at least one additive selected from the group consisting of an organic molybdenum compound, an organic fatty acid compound or an organic fatty acid derivative, and an organic phosphorus compound is added.
In order to accomplish the foregoing objects of the invention, the present invention also provides a rolling bearing comprising a plurality of rolling elements held rollably between an inner ring and an outer ring and the foregoing grease composition enclosed therein.
In order to accomplish the foregoing objects of the invention, the present invention further provides a rolling apparatus comprising a rolling element provided between an exterior member and an inner member wherein the rolling element rolls on a first contact surface at which the exterior member comes in contact with the rolling element and a second contact surface at which the interior member comes in contact with the rolling element, characterized in that the foregoing lubricating grease composition is enclosed therein.
The term xe2x80x9crolling apparatusxe2x80x9d as used herein is meant to indicate a linear guide or ball screw. The term xe2x80x9cexterior memberxe2x80x9d as used herein is meant to indicate a slider or guide rail for linear guide or nut for ball screw. The term xe2x80x9cinterior memberxe2x80x9d as used herein is meant to indicate a guide rail or slider for linear guide or screw axis for ball screw. Accordingly, in the case of linear guide, the first contact surface at which the exterior member comes in contact with the rolling element is the slider or the race on the guide rail while the second contact surface at which the interior member comes in contact with the rolling element is the race on the guide rail or the slider. In the case of ball screw, the race on the nut forms the first contact surface while the race on the screw axis forms the second contact surface.
The lubricating grease composition according to the invention uses, as the base oil in the basic grease composition, a synthetic oil capable of forming an oil film having a low viscosity so as to provide the excellent close contact property with respect to the rolling contact surface and the sliding surface. The base oil may preferably be a carbonic ester oil or a polyol ester oil. Accordingly, the low torque property, the wear impact resistance property, and the fretting resistance property can be enhanced. Moreover, since a lithium salt, preferably a lithium stearate salt is used as the thickener, formation of a lubricating film to be softened by application of a shearing stress at the time of rolling or sliding so as to provide the excellent adhesion property with respect to the rolling contact surface can be promoted.
In addition to the above-mentioned basic grease composition, since 0.5 to 10% by weight of at least one selected from the group consisting of an organic molybdenum compound, an organic phosphorus compound, and an organic fatty acid compound or an organic fatty acid derivative is added, the fretting wear resistance property, the low torque property, the impact resistance property, the wear resistance property, the impression resistance property, and the drop impact property by a dropping trouble, required particularly to a bearing for a HDD can be improved or provided.